1. Technical Field
The present invention is generally directed to a method and apparatus for supplying a continuous web of thermoplastic material and, more particularly, to a method and an apparatus for heat splicing two or more webs of an elastomeric thermoplastic film to form a continuous webbing which is supplied to a downstream line operation of a continuous manufacturing process.
2. Background Art
Various methods and apparatuses are currently known in the art for autogenously splicing (i.e., without adhesives) thermoplastic webbing or film to provide a continuous supply thereof. For example, various methods and apparatuses for butt welding thermoplastic sheets and films are disclosed in U.S. Pat. No. 3,956,047 which issued May 11, 1976 to Johnson. As disclosed, the method involves bonding a trailing end of one roll of thermoplastic film or sheet material to a leading end of another roll of such material by vertically superimposing the trailing and leading end portions of the two rolls and aligning the lateral edges of said portions over a significant distance sufficient to insure angular alignment of the two rolls at the butt weld. The two portions are severed along a specific transverse line and the severed portions are heated sufficiently to allow the portions to be welded together. The heated end portions are then brought together while maintaining the lateral edge alignment of the portions to form a single continuous sheet.
Alternatively, thermoplastic films or webs may also be spliced under the method disclosed in U.S. Pat. No. 4,129,469 which issued Dec. 12, 1978 to Deverell et al. Under the method disclosed, webs of thermoplastic films can be formed by splicing together two moving webs that are travelling at substantially equal linear speeds. The two moving webs are brought together into surface-to-surface contact and electrostatic charges are deposited upon one or both of the moving webs such that the webs are electrostatically bonded to each other.
Yet another method for splicing together two webs of thermoplastic film is disclosed in U.S. Pat. No. 3,700,532 which issued Jul. 15, 1968 to Pierson. According to the disclosed method, two thermoplastic films are positioned between an anvil and an ultrasonic horn that has planar non-parallel surfaces inclined at an acute angle. The films are stacked on the inclined surface in an overlapping relationship. Once the thermoplastic films have been overlapped, the ultrasonic horn is moved into contact with a portion of the upper film surface having an area at least as great as the area of overlap. Thereafter, ultrasonic vibrations are imparted by the horn to cause the thermoplastic film material to soften such that the overlapping portions unite and form a single film. After a specific period of time, the ultrasonic vibrations are discontinued and the spliced film is allowed to cool for permitting the softened portions of the thermoplastic films to harden. The horn is then withdrawn and the spliced film is removed for replacement with the next set of films.
While such prior art apparatuses and methods for splicing thermoplastic films together have addressed some of the problems associated with autogenously spliced thermoplastic films, they have not addressed the problems to the extent of, or in the manner of, the present invention. For example, and without intending to thereby limit the scope of the present invention, the known prior art has failed to address the problem of feeding a constant supply of an elastomeric thermoplastic film to a downstream line operation of a continuous high-speed manufacturing process while simultaneously splicing a second web of thermoplastic film to the original web of thermoplastic film upstream of the line operation. As will be appreciated, this ability to continuously run the line operation without interruptions or slow-downs leads to greater manufacturing efficiencies.